1. Field of the Invention
The present invention relates to communications, and, in particular, to allocation of communication channels in the presence of protected communication services in a wireless communication system.
2. Description of the Related Art
TV stations in the United States broadcast over a spectrum of frequencies within the UHF spectrum under licenses granted by the Federal Communications Commission (FCC), with other countries providing TV broadcast services in a similar manner over their own defined sets of government-allocated spectrum. To avoid interference, analog TV stations are spaced apart in frequency, and, since TV signals travel a long way, signals in adjacent areas are separated from each other. Digital TV reduces the bandwidth needs of TV broadcast providers because compression schemes such as MPEG reduce the bandwidth required for a single transmission. Broadcasters can either offer new channels within their spectrum allocations or use their spectrum allocation for high-definition signals, but at the same time, spectrum becomes available for the government to auction to other users. In addition, other types of devices with limited range, such as wireless microphones, are allowed to operate within these bands. However, within the Television (TV) spectrum, unused portions of frequency bands exist due to the spatial variation, frequency fragmentation, and temporal variation required for preventing licensed users (incumbent service providers) from interfering with one another. Recently, the required protection from interference between entities has been reduced using Digital TV as compared to analog TV.
The unused portions of the UHF Television (TV) spectrum, commonly known as “white space” represent frequency bands that might be employed by a growing number of network devices for wireless communication channels. These unlicensed devices, (“TV Band Devices” or “TVBDs”) might be allocated frequency bands to operate on these white space channels.
On Nov. 4, 2008 the FCC adopted a set of rules to allow these unlicensed devices to operate in the TV spectrum over a defined set of white spaces including 294 MHz of available bandwidth from channel 2 (512 MHz) to 51 (698 MHz), with the exception of channel 37. Other white spaces exist, and may be the subject of further FCC regulation in the future. The discussion of the FCC's reasoning for the creation of a new class of device, and the new rules allowing such new class of service, are described in a document, “Second Report and Order and Memorandum and Order,” released by the FCC on Nov. 14, 2008, and another document, “Second Memorandum Opinion And Order,” released by the FCC on Sep. 23, 2010.
As indicated by the FCC, low power devices might be permitted to operate in the TV bands on frequencies that are not being used by authorized services, enabling the development and operation of a wide range of new unlicensed wireless communications devices and systems. These new unlicensed wireless communications devices and systems can operate in white space frequency bands where signals are less subject to propagation losses than bands currently available for such devices. The propagation characteristics of the TV bands also allows devices to provide service at greater distance ranges than existing unlicensed devices.
However, the FCC mandates that new, unlicensed devices not interfere with the incumbent licensed service providers in the TV bands, such as TV broadcast stations, cable head-end services, and devices such as wireless microphones. Since unlicensed broadband devices share spectrum with broadcast TV and other licensed services, unlicensed broadband devices are required to incorporate a capability to avoid causing harmful interference to licensed services in the TV band. Specifically, an unlicensed device must determine whether a TV channel or portion of a TV channel is unused before it transmits. Fixed and personal/portable TVBDs that do not operate in client mode are required to access a central database system as part of such capability to ensure they do not interfere with TV or other licensed entities.
A central database system might be employed, and the process of allocating frequency bands or channels to TVBDs might be accomplished through a service operated by one or more white space allocation service providers. Whether operated by one provider or by multiple providers, a system should allocate substantially the same white space bands when a request from a TVBD device is received. However, given the size of the geographic area such as the United States, the number of incumbent licensed service providers and the number of bands possible, computation of permitted bands to allocate to a TVBD device request is large. A white space channel allocation service provider seeks to provide such channel information to the TVBD device relatively quickly, requiring significantly reduced server computation time when responding to a query by a device, in order to reduce cost and improve efficiency of providing the service.